Fluid energy machine

ABSTRACT

A fluid energy machine, comprising a crank drive (A) and a drive device which is mechanically connected to the crank drive, wherein the drive device has two electric motors, the respective output members of which are mechanically connected to the crank drive is disclosed. The fluid energy machine is arranged within a housing which seals the fluid energy machine with respect to the surroundings and which is connected to a pressure-holding system. A method for operating a fluid energy machine of this type is further disclosed.

The invention pertains to a fluid energy machine comprising a crank drive and a drive device that is mechanically connected to the crank drive, wherein the drive device comprises two electric motors, the respective output members of which are mechanically connected to the crank drive, as well as to a method for operating this fluid energy machine.

It is known to use so-called cryopumps or cryogenic high-pressure pumps, which are suitable for conveying a fluid in the low-temperature range, for refueling equipment such as motor vehicles with hydrogen that may be supplied in liquid form.

DE102007035616A1 discloses a pump that is particularly designed for cryogenic mediums. This pump comprises a piston-cylinder unit that is designed for conveying and/or compressing very cold fluids, e.g. hydrogen.

Such pumps are usually operated with a hydraulic drive. Other conventional low-temperature pumping devices comprise a rotary drive instead of the hydraulic drive, wherein said rotary drive is in turn coupled to the piston of the piston-cylinder unit.

The hydraulic drive for the low-temperature pumping device usually requires a relatively large structural volume for accommodating auxiliary units, as well as a cooling device and a reservoir for the hydraulic fluid. In addition, a pumping device with hydraulic drive is relatively expensive with respect to its installation and maintenance, as well as the measuring system to be installed for the position measurement in the hydraulic cylinder. To this end, a linear position measuring system is usually provided. A sine-like acceleration profile of the piston has to be adjusted in the pumping device in order to avoid impermissible peak values of the volume flow to be generated. When using a hydraulic drive device, the realization of a corresponding acceleration profile is associated with increased costs for the required control, as well as the control system to be installed therefor. In addition, hydraulic drive devices usually do not make it possible to realize reciprocating motions of the piston-cylinder unit with a frequency of more than approximately 2 Hz.

In an variation comprising an electric motor drive in combination with a crank drive, the maximum frequency-dependent nominal torques of commercially available electric motors limit the maximum capacity of the pumping device with respect to the attainable rate of flow, as well as the attainable delivery pressure. If it is attempted to achieve a high rate of flow and a high delivery pressure, corresponding frequencies of the reciprocating motions, as well as forces or torques, have to be applied to the crank drive by the electric motor. This means that corresponding counter-forces respectively act upon the electric motor or its mounting and/or upon the mounting of a torque-transmitting machine element between the electric motor and the crank drive. The stability of the mounting points has to be adapted accordingly if they should not be subjected to corresponding wear, which particularly becomes noticeable when the output member of the electric motor is essentially arranged coaxial to the rotational axis of the crank drive and rigidly connected to this crank drive.

A fluid energy machine suitable for resolving these disadvantages comprises a crank drive and a drive device that is mechanically connected to the crank drive, wherein a torque can be introduced into the crank drive by said driving device. The fluid energy machine additionally comprises a piston-cylinder unit, the piston of which is mechanically connected to the crank drive. It is proposed that the drive device comprises two electric motors, the respective output members of which are mechanically connected to the crank drive. It is furthermore proposed that the piston-cylinder unit comprises only one piston and only one cylinder. The electric motors, which are also simply referred to as motors below, are realized in the form of rotatory motors, wherein the arrangement of more than two motors would also be conceivable. The drive device therefore comprises at least two motors.

One advantage of such a fluid energy machine can be seen in that it operates despite slow rotational speeds of the shaft between 1 and 600 revolutions per minute (rpm) and nevertheless can generate the required high pressures. Despite the slow rotational speeds, a high torque in the range between 1000 and 8000 Nm, particularly up to 4000 Nm, can be achieved with the electric motors. The force exerted upon the piston rod as a result of this torque lies between 10 and 150 kN, particularly between 15 and 20 kN. Since two motors are connected to the crank drive, a symmetric load and a distribution of the counter-forces or counter-torques over both motors or their driveshafts is respectively achieved such that the overall load and/or wear on the drive device and the crank drive can be reduced. The mountings can have correspondingly smaller dimensions or the shafts can be realized with a smaller diameter, respectively.

The disadvantage of such a fluid energy machine is that its installation in explosion protection zones of the categories I and II is not possible due to the lack of suitable electric motors currently available on the market. However, this is particularly important for conveying hydrogen and other combustible substances.

The invention is based on the objective of disclosing a fluid energy machine and a method for operating a fluid energy machine, which can be used in explosion protection zones of the categories I and II.

With respect to the device, this objective is attained in that the fluid energy machine is arranged within a housing, which seals the fluid energy machine relative to the environment and is connected to a pressure retention system.

The electric motors used are advantageously water-cooled electric motors. In this way, no air supply for cooling the motors is required and the seal of the housing can thereby be simplified.

With respect to the method, the above-defined objective is attained in that the fluid energy machine is arranged within a housing, through which a pressurized medium flows. The housing is preferably realized in the form of a load-bearing housing.

The housing is preferably divided into multiple compartments, wherein the compartments are connected to one another. The compartments are advantageously connected to one another in series. The pressurized medium preferably flows through the compartments successively.

In a preferred embodiment, the housing is divided into three or five compartments, wherein a first compartment encloses the crank drive and a lead-through is provided for connecting the crank drive to the piston-cylinder unit. All lead-throughs of the housing are sealed relative to the environment by means of sealing mechanisms familiar to a person skilled in the art. Covers, sealing grooves with sealing rings, adhesive seals and sealed screws particularly may be used for this purpose.

Two other compartments respectively represent the outer compartment of the respective electric motor. The respective magnets, coils and power electronics are particularly accommodated in these compartments. These compartments are particularly provided with lead-throughs for the cooling system and the power supply, as well as the control systems. In a preferred embodiment, two additional compartments respectively form the inner compartments of the two electric motors. The connection of the respective shaft for the power transmission of the respective motor is located within these compartments. These compartments are sealed relative to the atmosphere by means of additional cover caps with special seals and make it possible to lead through the shafts. In another preferred embodiment, however, the electric motors may also be arranged within one compartment only.

The housing is particularly realized in such a way that an excess pressure between 0.01 and 50 mbar, particularly 2.5 mbar, can be applied. This means that the seals for sealing all lead-throughs are realized in such a way that no pressurized medium escapes if the pressure in the interior of the housing exceeds the pressure in the environment of the fluid energy machine by 0.01 to 50 mbar, particularly 2.5 mbar. In a preferred embodiment, in which the housing is sealed relative to the environment, the excess pressure can also be generated if no constant throughflow takes place.

The housing is advantageously connected to the pressure retention system by means of an inlet and an outlet. The inlet is preferably arranged on the first compartment and the outlet is installed on the last compartment, particularly the fifth compartment. The compartments are connected to one another by means of bores in such a way that all hollow spaces are connected to one another and a pressurized medium can flow through these hollow spaces.

The pressure retention system advantageously maintains an excess pressure of the pressurized medium. The pressure retention system is preferably realized in the form of a compressor station or a cylinder rack. In case pressurized medium escapes from the housing into the environment due to a small leak and thereby leads to a loss of pressurized medium, new pressurized medium can be introduced by means of the pressure retention system. Consequently, the pressurized medium advantageously does not have to flow through the housing continuously, but new pressurized medium preferably is only added each time the excess pressure in the housing drops below a predefined value.

Air, nitrogen or another inert gas is advantageously used as pressurized medium. The pressurized medium preferably flows through the housing with an excess pressure between 0.01 and 50 mbar, particularly 2.5 mbar.

Due to the excess pressure, no reactive mixture can flow into the housing from outside such that the electric motors, which represent a potential ignition source, are protected and the fluid energy machine therefore can be installed and used in explosion protection zones.

Sensors for monitoring the pressure of the pressurized medium can be advantageously provided within the pressure retention system and/or within the housing. If it is detected that the pressure deviates from a predefined value, e.g. in the form of a pressure loss, this is indicative of a leak. The sensors are advantageously connected to the electric motors such that they can be switched off and deenergized. In this way, the electric motors would no longer represent an ignition source.

It would furthermore be possible to provide sensors that detect traces of the medium to be conveyed within the pressurized medium in order to detect a leak within the housing. In this way, small leaks of the medium to be conveyed by the fluid energy machine can already be detected. In addition, the usually combustible medium to be conveyed is diluted with the pressurized medium and discharged from the system. The risk of explosions can thereby be reduced.

The fluid energy machine can be stopped if a predefined limiting value is exceeded.

After a standstill of the fluid energy machine and/or the pressure retention system, the system is preferably flushed with an increased flow of the pressurized medium for a certain period of time, particularly 2 to 5 minutes, in order to remove potential contaminations.

The fluid energy machine is advantageously used for generating a hydrogen volume flow and for compressing hydrogen. It is preferably used for refueling a vehicle with liquid or gaseous hydrogen. In this case, the hydrogen is compressed to a system pressure of 50-1000 bar, particularly to 350-500 bar or 700 or 900 bar. The discharge rate of the hydrogen is preferably adjusted with the frequency of the electric motors such that it lies between 0 and 250 kg/h, particularly between 30 and 200 kg/h.

The invention is described in greater detail below with reference to an exemplary embodiment that is schematically illustrated in FIG. 1.

FIG. 1 schematically shows an embodiment of the inventive device. This figure shows the housing of a high-pressure pump in the form of an explosion-protected design. The pump is suitable for cryogenic fluids, particularly for hydrogen.

The housing is divided into compartments 1-5, wherein the compartments are connected to one another. The compartment 1 encloses the crank drive A. The compartment 2 and the compartment 4 respectively represent the outer compartments of the respective electric motors M. The respective magnets, coils and power electronics are particularly accommodated in these compartments. The compartment 3 and the compartment 5 respectively form the inner compartments of the two electric motors M. The connection of the respective shaft for the power transmission of the respective motor is located within these compartments. These compartments are sealed relative to the atmosphere by means of additional cover caps W with special seals.

All hollow spaces within the respective compartments are fluidically accessible through bores. Consequently, all hollow spaces within the housing can be reached by a pressurized medium and thereby flushed.

A pressurized medium is introduced into the housing through the supply line for the pressurized medium E, which is arranged in the compartment 1 in this exemplary embodiment. The pressurized medium successively flows through all compartments 1-5 and is once again returned to the pressure retention system in the compartment 5 through an outlet D.

The pressure retention system is designed for maintaining the pressurized medium at a pressure of 2.5 mbar. In case pressurized medium escapes into the environment due to small leaks, additional pressurized medium can be supplied by means of the pressure retention system. An emergency shutdown is initiated if a pressure drop in the pressure retention system or an excessively high hydrogen content of the pressurized medium is detected. The motors are stopped and deenergized. In this way, the motors no longer represent an ignition. source. The system can be restarted after corresponding maintenance work has been performed.

When the pressure retention system is initially started or restarted after a standstill, the pressure retention system is flushed with an increased mass flow of the pressurized medium for a defined period of time, particularly 2 min. Any hydrogen that has escaped from the pump or the lines into the housing during the standstill is thereby removed or at least diluted. 

1. A fluid energy machine comprising a crank drive and a drive device that is mechanically connected to the crank drive, wherein the drive device comprises two electric motors, the respective output members of which are mechanically connected to the crank drive, characterized in that the fluid energy machine is arranged within a housing, which seals the fluid energy machine relative to the environment and is connected to a pressure retention system.
 2. The fluid energy machine according to claim 1, characterized in that the housing is divided into multiple compartments, wherein the compartments are connected to one another.
 3. The fluid energy machine according to claim 1, characterized in that the housing is connected to the pressure retention system by means of an inlet and an outlet.
 4. The fluid energy machine according to claim 1, characterized in that that an excess pressure between 0.01 and 50 mbar.
 5. A method for operating a fluid energy machine comprising a crank drive and a drive device that is mechanically connected to the crank drive, wherein the drive device comprises two electric motors, the respective output members of which are mechanically connected to the crank drive, characterized in that the fluid energy machine is arranged within a housing, through which a pressurized medium flows.
 6. The method according to claim 5, characterized in that an inert gas selected from the group consisting of air and nitrogen is used as pressurized medium.
 7. The method according to claim 5, characterized in that the pressurized medium flows through the housing with an excess pressure between 0.01 and 50 mbar.
 8. The method according to claim 5, characterized in that the excess pressure of the pressurized medium is maintained with a pressure retention system.
 9. The method according to claim 5, characterized in that the housing is divided into multiple compartments, which are connected to one another and through which the pressurized medium flows successively.
 10. The method according to claim 5, characterized in that the fluid energy machine is used for generating a hydrogen volume flow and/or for compressing hydrogen.
 11. The method according to claim 7, characterized in that the pressurized medium flows through the housing with an excess pressure of 2.5 mbar. 